Rewrite the studio server. Keeps the same API endpoints but the entire code is redone

List of things not working as of today now

FLOW + CMS

[x] [POST] http://localhost:3300/api/v1/cms/:contentType/elements - 404
- It seems like we use the same call to save and list content-elements?
[x] [POST] http://localhost:3300/api/v1/cms/elements/bulk_delete - 404
- Delete a singl or multiple content-elements
[x] [POST] http://localhost:3300/api/v1/cms/elements - 400
- "body.from" is not allowed
- Search on all content-elements (also valid for specific elements)
  NLU
[x] [POST] http://localhost:3300/api/v1/nlu/intents - 404
- Edit or create an intent
[x] [POST] http://localhost:3300/api/v1/nlu/entities/:entityId - 404
- Edit an existing entity
[x] [POST] http://localhost:3300/api/v1/nlu/entities/ - 404
- Creates a new entity
  QnA
[ ] [GET] http://localhost:3300/api/v1/qna/export - 404
- Export QnAs to JSON
[ ] [POST] http://localhost:3300/api/v1/qna/questions/:qnaId - 404
- Create or edit a QnA
[ ] [POST] http://localhost:3300/api/v1/qna/questions/:qnaId/delete - 404
- Delete a QnA
[x] [GET] http://localhost:3300/api/v1/qna/contentElementUsage - 404
- Visit the page
  Config
[x] [POST] http://localhost:3300/api/v1/config - 404
- Save the config
[x] [POST] /media - 404
- Any calls to the media storage (ex: add an avatar to bot)

Closes DEV-2687